1. Field of the Invention
The present invention relates to a new class of high hyperpolarizability organic chromophores and a process for synthesizing the same and, more particularly, pertains to polymeric electro-optic modulators and switches prepared by incorporating organic .pi.-electron chromophores covalently into electrically-poled polymeric materials.
2. Description of the Related Art
Numerous materials have been proposed for use in electro-optic devices. These include inorganic materials such as lithium niobate, semiconductor materials such as gallium arsenide, organic crystalline materials, organic materials prepared by sequential synthesis methods, and electrically-poled polymer films containing organic chromophores incorporated either physically to form composites or chemically to form homopolymer materials. A general review of nonlinear optical materials and their technological applications is provided in L. Dalton, "Nonlinear Optical aterials", Kirk-Othmer Encyclopedia of Chemical Technology, 4th Edition, Volume 17 (John Wiley & Sons, New York, 1995) pp. 288-302; in H. S. Nalwa and S. Miyata, Nonlinear Optics of Organic Molecules and Polymers, (CRC Press, Boca Raton, 1997) p. 1-884; in P. N. Prasad and D. J. Williams, Introduction to Nonlinear Optical Effects in Molecules and Polymers, (John Wiley & Sons, New York, 1991; and in D. M. Burland, "Second-Order Nonlinearity in Poled Polymer Systems", Chemical Reviews, Vol. 94, pages 31-75 (1994)).
Electro-optic materials contain highly polarizable electrons. When an electric field is applied to these materials, the electron polarization changes significantly resulting in an increase in index of refraction of materials and a decrease in the velocity of light passing through the materials. This electric field-dependent material index of refraction can be used to impose electric signals onto optical signals, to switch optical signals in a local area network, or to steer a beam of light. The most commonly used material is currently lithium niobate. This material possesses an electro-optic coefficient on the order of 35 pm/V which results in a typical drive voltage (called V.sub..pi. --the voltage required to produce a .pi. phase shift of light) of on the order of 5 volts. Lithium niobate has a high dielectric constant which results in velocity mismatch of electric and optical waves propagating in the material. This mismatch necessitates a short interaction length (making reduction of drive voltage by increasing device length unfeasible) and limits the bandwidth of the device, for example, a one centimeter electro-optic modulator constructed from lithium niobate typically has a bandwidth of less than 10 Gigahertz. As lithium niobate is a crystalline material, integration with semiconductor electronics and silica fiber optics typically requires sophisticated coupling techniques such as flip-chip bonding and in-diffusion. An electro-optic material that does not suffer from the foregoing limitations would be very desirable.